1. Field of the Invention
The present invention relates to improvements in a method of and an apparatus for manufacturing a tape-formed oxide superconductor.
2. Description of Related Art
Heretofore, as a method of manufacturing a tape-formed oxide superconductor of YBCO type (Y—Ba—Cu—O) suitable for applications to superconducting magnets, superconducting cables, and electric power machines and instruments, there has been known one based on organometallic salt coating and thermodecomposition (or MOD short for metal organic deposition) capable of manufacturing the tape-formed oxide superconductor by a non-vacuum process.
With this method, a superconducting layer is formed in such a way that an intermediate layer is formed on a substrate, that the substrate bearing the intermediate layer is coated with that mixed solution of trifluoroacetate salt (TEA salt) or the like metalorganic acid salt such as octylic acid salt or naphthenic acid salt in which individual metal elements constituting the superconductor are contained at predetermined mol ratios, and that the resulting substrate is calcined, followed by a heat treatment.
In order to make such a tape-formed oxide superconductor elongate, a tubular furnace is employed as a treatment furnace. Heretofore, an atmosphere in the furnace has been controlled by causing an atmosphere gas (reactive gas) to flow from one end to the other end of a furnace core tube. It has been known that, when the gas is caused to flow to the elongate material in the axial direction of the furnace core tube in this manner, the atmosphere changes in the axial direction of the furnace core tube under the influence of a gas which is generated from the elongate material during a reaction, so the elongate material becomes very difficult of being uniformly reacted.
Especially in a method (TFA-MOD method) wherein a YBCO film is formed in such a way that the film of a preform obtained by the calcination of the above TFA salt and containing F (ex-situ method) is formed on a tape surface, and that it is thereafter heat-treated, HF is generated during the calcination and the heat treatment for the reasons that the element F is contained in the preform film and that water vapor is used during the heat treatment. This poses the problem that superconducting characteristics degrade under the influence of HF gas generated after the reaction.
For the purpose of suppressing the influence of the gas after the reaction and holding the atmosphere in the furnace constant in order to avoid such a problem, the reactive gas needs to flow along the tape surface in a direction vertical to the axial direction of the furnace core tube.
As an atmosphere control type heat treatment furnace wherein the reactive gas is caused to flow along the tape surface in the direction vertical to the axial direction of the furnace core tube, there has been known one in which a plurality of gas flow passages are formed by a furnace core tube that is configured of an outer tube and an inner tube arranged concentrically, and partition plates that divides a cylindrical space defined by the outer tube and the inner tube, into a plurality of parts within a section vertical to the axial direction of the furnace core tube, and in which pluralities of gas outflow ports and gas inflow ports are respectively provided at substantially the opposing positions of the inner tube in the plurality of gas flow passages (refer to Patent Document 1).    Patent Document 1: JP-A-2003-121076 (page 2, right column, lines 24-31 and lines 37-41, and FIGS. 1-4)
In the atmosphere control type heat treatment furnace wherein the reactive gas is caused to flow along the tape surface in the direction vertical to the axial direction of the furnace core tube, the homogeneous gas is supplied at different flow velocities to the gas flow passages having the pluralities of gas outflow ports and gas inflow ports, whereby a pressure difference can be established between the gas outflow ports and the gas inflow ports, and the reactive gas can be caused to uniformly flow along the tape surface in the direction vertical to the axial direction of the furnace core tube.
Regarding the above method, however, the following fact has been revealed: When a tape-formed wire material in which a film body being a superconductor preform is formed on a substrate of large area (large width) is caused to continuously travel in the furnace, so as to react the film body into a superconducting layer, the growth rate of a crystal differs in the widthwise direction of the tape. More specifically, the crystal growth rate on the discharge side of a gas after the reaction becomes much lower as compared with that on the supply side of the reactive gas. It is accordingly difficult to form a superconducting layer which as uniform characteristics in the widthwise direction of the surface of the substrate.
There has consequently been the problem that a tape-formed oxide superconductor of large area (large width) is difficult of being obtained.